The overlap is produced mainly by relatively high birth rates among a few of the more developed areas-rates which are now declining.
Among the more developed areas, Oceania, with a relatively small population, increased most rapidly between 1920 and 1960, rising from 8.5 to 15.7 million, or by about 85 percent. Northern America increased from 116 to 199 million, a gain of about 75 percent. Next in growth rate, despite great losses during World War II, was the Soviet Union with a population of 155 million in 1920 and 214 million in 1960, an increase of about 38 percent. Lowest in growth rate was Europe (excluding the U.S.S.R.) which, with a population of 325 million in 1920 and 425 million in 1960, had an increase of about 30 percent.
Among the less developed areas, Latin America showed the greatest population growth, from 90 million in 1920 to 212 million by 1960. More than doubling, it increased by 135 percent. Africa registered the next greatest growth, having 143 million persons in 1920 and 273 million in 1960, an increase of about 91 percent. South Asia, with 470 million in 1920 and 865 million in 1960, increased by 84 percent. (However, the estimated difference between Africa and south Asia is well within a statistical margin of error.) Slowest in population growth among the less developed areas was east Asia with an estimated 553 million in 1920 and 794 million in 1960, an increase of about 43 percent. It must be noted, however, that the data for east Asia are most uncertain.
The United Nations has also analyzed the growth rates of the world divided into Northern Areas and Southern Areas, with the Tropic of Cancel-serving as the dividing line. The Southern Areas (south Asia, Africa, Latin America, and Oceania) as a group grew more rapidly than the Northern Areas. They almost doubled, increasing from 711 million persons in 1920 to 1.4 billion in 1960. The Northern Areas, in contrast, rose from 1.2 billion persons in 1920 to 1.6 billion in 1960, an increase of 33 percent.
WORLD POPULATION PROSPECTS
In 1966, the United Nations issued revised population projections for the world, and for the developed and developing areas, to the end of the century (10, pp. 13-18, 135). The projections indicate that if present fertility and declining mortality rates were to continue, world population would reach 7.5 billion by 2000.
Three other projections are calculated by the United Nations based on varying declines in the birth rate with different timing. These projections are published as "high, low, and medium variant projections." The high variant gives a world population in 2000 of 7 billion, the medium 6.1 billion, and the low 5.4 billion.inish further.